The steam vent line on my motor comes off of the fronts of the two heads and is plumbed to go through the throttle body. For the longest time I ran it just plugged and the motor ran at ok temps. The only over heats were due to my electric fans not turning on. without the steam vent line hooked up it was also a giant pain in the ass to get the air bled out of. It'd overheat just idling after a coolant refill and I'd have to shut it down, let it cool, run it again, shut it down, let it cool,ect. Eventually it'd get to where most of the air was bled out.
Anyways, this summer I figured it might be time to install the proper stem vent line, so I bought an upper radiator hose "adapter" that allowed me to tee in the steam vent line to the upper hose. I got it from www.jagsthatrun.com
. Now the cooling system bleeds much nicer, but otherwise I really didn't notice any real difference. I guess that a tee into the upper hose is how several gm motors do it so the method is fine.
One thing that people say is that without the steam vent lines, hot spots in the heads can develop and you would never see it on a water temp Gage. I am not totally sure that is true.
Anyways, the upper radiator hose tee is as easy as a click to buy, and only requires a small amount of coolant loss to install so I figure why not use it.
The reason I didn't is because I followed the advice of several folks that said it was not necessary...... As far as the swap goes, the best advice I think I have ever gotten is to run the motor as close to stock as possible and issues should be minimized...... This is one of those things that makes it more like the factory did it.